Find the fourth proportional to 12, 18, 20.

Options

A. 30
B. 50
C. 35
D. 40

Answer

To find the fourth proportional to the numbers 12, 18, and 20, we can follow these steps:

### Step 1: Set up the proportion
We start by expressing the relationship between the numbers in proportion form. We want to find a number \( x \) such that:
\[ \frac{12}{18} = \frac{20}{x} \]

### Step 2: Cross-multiply
To solve for \( x \), we can cross-multiply:
\[ 12 \cdot x = 18 \cdot 20 \]

### Step 3: Calculate the right side
Now, calculate \( 18 \cdot 20 \):
\[ 18 \cdot 20 = 360 \]
So, we have:
\[ 12x = 360 \]

### Step 4: Solve for \( x \)
Now, divide both sides by 12 to isolate \( x \):
\[ x = \frac{360}{12} \]

### Step 5: Perform the division
Calculating \( \frac{360}{12} \):
\[ x = 30 \]

### Conclusion
Thus, the fourth proportional to 12, 18, and 20 is:
\[ \boxed{30} \]